The present invention relates to a smoke detector.
Smoke detectors for detecting smoke through detection of scattered light by smoke particles have conventionally been proposed and put into practice. Such a smoke detector detects a fire as follows. The smoke detector has a dark chamber for storing a photo emitter and a photo detector. Light emitted from the photo emitter is scattered by smoke particles having flowed into the dark chamber, to thus generate scattered light. The photo detector receives the scattered light.
In recent years, smoke detectors including light traps for inhibiting noise light (light generated by reflection, by an inner wall of the dark chamber, of light having been emitted from the photo emitter) from reaching the photo detector are disclosed in, for example, Japanese Patent Publication Nos. 11-248628A, 2000-65740A and 2000-65741A. When such a smoke detector is adopted, noise light can be caused to enter the light trap, to thus attenuate the noise light. Hence, incidence of the noise light to the photo detector is suppressed, thereby enabling an increase in an S/N ratio to a certain extent.
However, in the smoke detector disclosed in Japanese Patent Publication No. 11-248628A, the light trap is disposed in front of the photo emitter and the photo detector. Therefore, light emitted from the photo emitter is reflected in a direction parallel to a virtual plane including an optical axis of the photo emitter and that of the photo detector. Accordingly, since noise light is easily incident to a light detecting region, occurrence of a false alarm remains highly possible.
The smoke detectors disclosed in Japanese Patent Publication Nos. 2000-65740A and 2000-65741A employs a labyrinth structure for inhibiting light from entering the dark chamber. Since light emitted from the photo emitter is reflected by edge sections of wall members constituting the labyrinth structure, irregular noise light of an amount that cannot be sufficiently attenuated by the light trap is generated. Therefore, the noise light may enter the light detecting region, to thus cause a false alarm.
In addition, in the smoke detectors disclosed in Japanese Patent Publication No. 11-248628A, a plurality of light traps must be disposed; and in the smoke detector disclosed in Japanese Patent Publication Nos. 2000-65740A and 2000-65741A, a light trap must be disposed inside the labyrinth structure within the dark chamber. Accordingly, either case requires a large space for disposing the light trap, whereby miniaturization of the smoke detector has encountered difficulty. In addition, the smoke detector disclosed in Japanese Patent Publication No. 2000-65741A includes another member such as a lens in addition to the light trap, whereby the cost for manufacturing the smoke detector may be increased. Furthermore, the light trap and/or the lens may inhibit smoke from flowing into the dark chamber.